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Table of Contents
Network & Messaging Cheat Sheet
Network Models
| OSI Model | TCP/IP Model | Purpose |
|---|---|---|
| Layer 7: Application | Application | Application protocols |
| Layer 6: Presentation | Application | Serialization, encryption |
| Layer 5: Session | Application | Session management |
| Layer 4: Transport | Transport | End-to-end communication |
| Layer 3: Network | Internet | Routing |
| Layer 2: Data Link | Link | Local network communication |
| Layer 1: Physical | Physical | Signal transmission |
Layer 7: Application
Purpose: Define application rules and message formats.
Examples Protocol:
* HTTP / HTTPS * WebSocket * Redis Protocol (RESP) * AMQP (RabbitMQ) * Kafka Protocol * SMTP * FTP * DNS * MQTT
Examples of messages:
GET /orders HTTP/1.1
XREAD BLOCK 2000 STREAMS orders $
Fetch Request
Layer 6: Presentation
Purpose: Format, serialize, compress, and encrypt data.
Examples:
* JSON * XML * Protobuf * Avro * UTF-8 * Gzip * TLS/SSL
Example:
HTTP + TLS = HTTPS
Layer 5: Session
Purpose: Establish, maintain, and terminate sessions.
Examples:
* HTTP Keep-Alive * WebSocket Session * Session IDs * Authentication Sessions
Layer 4: Transport
Purpose: Deliver data between processes.
Transport-layer protocols.
TCP
* Connection-oriented * Reliable delivery * Ordered messages * Retransmission support
Used by:
* HTTP/1.1 * HTTP/2 * WebSocket * Redis * RabbitMQ * Kafka
UDP
* Connectionless * Faster * No delivery guarantee
Used by:
* DNS * VoIP * Online games * WebRTC * QUIC (HTTP/3)
Layer 3: Network
Purpose: Route packets between networks.
Protocols:
* IPv4 * IPv6 * ICMP
Example IP:
192.168.1.10
Devices:
* Router
Layer 2: Data Link
Purpose: Transfer frames within a local network.
Protocols:
* Ethernet * Wi-Fi * ARP
Example MAC address:
AA:BB:CC:DD:EE:FF
Devices:
* Switch
Layer 1: Physical
Purpose: Transmit raw bits.
Examples:
* Network cables * Fiber optics * Radio waves * Electrical signals
010101010101
Connection vs Protocol
Protocol = language Connection = communication channel
Examples:
HTTP + TCP WebSocket + TCP RESP + TCP AMQP + TCP Kafka + TCP HTTP/3 + QUIC + UDP
Messaging Systems
| System | Application Protocol | Transport | Communication Model |
|---|---|---|---|
| Redis Streams | RESP | TCP | Pull + Long Polling |
| Redis Pub/Sub | RESP | TCP | Push |
| RabbitMQ | AMQP | TCP | Push |
| Kafka | Kafka Protocol | TCP | Pull + Long Polling |
Who Calls Who?
Database Polling
Worker → Database
Worker repeatedly asks:
SELECT * FROM jobs WHERE STATUS = 'pending';
Redis Streams
Worker → Redis
Worker sends:
XREAD BLOCK 2000
Redis waits up to 2 seconds, then replies.
Redis Pub/Sub
Worker → Redis (SUBSCRIBE) Redis → Worker (messages)
Redis pushes messages to subscribers.
RabbitMQ
Worker → RabbitMQ (basic.consume) RabbitMQ → Worker (messages)
RabbitMQ pushes messages.
Kafka
Worker → Kafka (Fetch Request) Kafka → Worker (response)
Consumer repeatedly sends fetch requests.
TCP Connection Behavior
| System | Persistent TCP | Repeated Requests | Server Push |
|---|---|---|---|
| Database Polling | Optional | Yes | No |
| Redis Streams | Yes | Yes (XREAD) | No |
| Redis Pub/Sub | Yes | No | Yes |
| RabbitMQ | Yes | No | Yes |
| Kafka | Yes | Yes (Fetch Request) | No |
Redis Streams
XREAD BLOCK
Example:
XREAD BLOCK 2000 STREAMS orders $
Meaning:
* Read from stream orders
* Wait up to 2000 ms if there is no data
* Return immediately when a message arrives
* Reuse the same TCP connection
Flow:
TCP Connection #1 ├── XREAD BLOCK 2000 ├── XREAD BLOCK 2000 ├── XREAD BLOCK 2000 └── ...
Kafka
Fetch Request
Consumer sends:
Fetch messages from: - topic: orders - partition: 0 - offset: 123
Kafka:
* Waits for new data * Returns immediately if data exists * Returns empty response after timeout * Keeps using the same TCP connection
Flow:
TCP Connection #1 ├── Fetch Request ├── Fetch Request ├── Fetch Request └── ...
HTTP vs WebSocket
| Feature | HTTP/1.1 | HTTP/2 | WebSocket |
|---|---|---|---|
| TCP | Yes | Yes | Yes |
| Persistent Connection | Keep-Alive | Yes | Yes |
| Multiplexing | No | Yes | N/A |
| Client Initiates | Yes | Yes | Initial only |
| Server Push Anytime | No | No | |
| Full Duplex | No | No | Yes |
HTTP/3
HTTP/1.1 → TCP HTTP/2 → TCP HTTP/3 → QUIC → UDP
Key Takeaways
* TCP provides reliable communication. * Application protocols define message meaning. * Redis Streams and Kafka use pull + long polling. * Redis Pub/Sub and RabbitMQ use push. * WebSocket provides bidirectional communication. * HTTP/2 is not WebSocket. * HTTP/3 uses QUIC over UDP.